function zurueck() {
	  var woher=document.referrer;
	  var stelle=woher.lastIndexOf("//") + 2;

	  if (navigator.appName == 'Netscape') {			/* fuer Netscape */
		  if (woher=="" || woher.substr(stelle,3)=="www")
		  window.location.href="index.html"
		  else history.back();
	  }
	  else if (document.all != null) {				/* fuer Internet Explorer */
		if (woher!="") window.location.href="index.html"
		else history.back();
	  }
	}